32 



NEW YORK STATE MUSEUM 



Mount Marcy quadrangle comparable with those on Lake Sanford 

 to the west, where it forms important bodies of ore. 



Three analyses are available of the anorthosite from localities 

 within the Mount Marcy quadrangle. Two were made by Prof. 

 Albert B. Leeds (i and 2 below). The sample for i was the coarsely 

 crystalline variety of uncrushed feldspar from the summit of Mount 

 Marcy. No. 2 is the granulated variety and was regarded by Doctor 

 Leeds as the ground mass of a porphyritic rock. The locality is not 

 stated in his paper. No. 3 has been specially made for this bulletin 

 by Dr C. A. Joiiet, at the time of the department of chemistry at 

 Columbia University. The analysis was based on a large sample 

 from the High Fall, Giant Trail. The rock was a more pyroxenic 

 variety than the other two. 



SiO, 





I 

 54-47 



2 

 54-62 



3 



52.37 



AUO3 





26.45 



26.50 



24.68 



Fe^Os 





1.297 



0.757 



1.24 



FeO 





0.665 



0.565 



3-49 



MgO 





0.69 



0.74 



2.00 



CaO 





10.80 



9.88 



10.57 



NajO 





4-37 



4-50 



4.02 



K2O 





0.92 



1.23 



0.86 



H.0+ 





0.53 



0.91 



0.90 



Total 



100.192 



99.702 



100.13 



Sp. gray. 





2.72 



2.70 



not det. 



Quartz 





1.62 



1.56 



Deficit .90 



Orthoclase 





S.004 



7-23 



5.00 



Plagioclase 





84.186 



82.20 



80.52 



Magnetite 





1.856 



•93 



1.62 



Kaolinite 





2.58 



3.S7 





Water 





.15 



. II 



.90 



Diopside and hypersthene 4.616 



4.30 



12.86 



Light-colored 



minerals 



6.472 



93-97 



85.52 



Dark-colored 



minerals 



93-39 



5-23 



14.48 



Plagioclase 





Abi An3 



Abi An2.4 



Abi An->.at 



1 Anorthosite, summit of Mount Marcy, A. B. Leeds, N. Y. State Mus. 

 30th Ann. Rep't, 1878, p. 92. 



2 Anorthosite, granulated variety. Probably Keene valley. A. B. Leeds, 

 as under i. 



3 Pyroxenic anorthosite, High Fall, Giant Trail, C. A. Joiiet, for this 

 bulletin. Previously published in N. Y. State Mus. Bui. 138, p. 36, 1910. 



All these analyses show that the rock is nearly all labradorite, but 

 that minor though variable amounts of the bisilicates and magnetite 

 are associated. Doctor Leeds in discussing his two analyses develops 

 the elaborate calculations which were practised by the mineralogists 

 and petrographers of forty years ago, and which have become so 

 much simplified in the years since then. 



